R/gapfillStreamflow.R

In CityWaterBalance: Track Flows of Water Through an Urban System

#' Fill gaps in streamflow records
#' 
#' This function fills in gappy streamflow records using a median of discharge
#' ratio from master gages.   
#' 
#' @param flowlist list of gage data and information from getStreamflow
#' @param paired_gages list of gage pairs where pair <- c(gappy,master)
#' @return list of: 
#'  \item{sites}{list of gage site names}
#'  \item{site_num}{list of gage numbers}
#'  \item{flows}{xts of gap-filled daily average discharge}
#' @importFrom stats median
#' @examples 
#' gages <- c('05551540', '05552500')
#' flow <- getStreamflow('2000-01-01', '2010-12-31', gages)
#' flow <- gapfillStreamflow(flow, list(c(gages[1], gages[2])))
#' @export


gapfillStreamflow <- function(flowlist, paired_gages) {
    
    sites <- flowlist$sites
    sn <- flowlist$site_num
    f <- flowlist$flows
    
    for (i in 1:length(paired_gages)) {
        
        gages <- paired_gages[[i]]
        
        gappy <- gages[1]
        master <- gages[2]
        
        j <- which(sn == gappy)
        k <- which(sn == master)
        
        a <- stats::median(f[, j]/f[, k], na.rm = TRUE)  # ratio of gappy:master flows
        
        gaps <- which(is.na(f[, j]))
        f[gaps, j] <- f[gaps, k] * a
        
    }
    
    names(f) <- sn
    
    return(list(flows = f, sites = sites))
    
}